1. Field of the Invention
This invention relates generally to closures, and more specifically to an improved closure for protecting the external threads at the end of a pipe or the like.
2. Description of the Prior Art
It is known in the prior art to provide a plastic closure for protecting the external threads at the end of a pipe. The closure comprises a generally tapered sleeve which in its normal uncompressed condition is mounted over the threads on the pipe. The sleeve is compressed by tightening a metal strap enclosing the sleeve for urging straight threads on its inner peripheral surface into engagement with the external pipe threads for tightly securing the closure to the pipe end. One disadvantage of this prior art closure is that it does not readily permit screwing or unscrewing the closure from the external threads when the closure is in its compressed condition. Another disadvantage is that the peripheral strap seat is conical relative to the axis of the sleeve when the sleeve is compressed. This results in an uneven distribution of the radially inwardly directed forces on the seat when the strap is tightened and also in possible damage to the seal on the strap. Another disadvantage of such closure is that the strap seal rests on a curved surface resulting in a curved and weakened seal when the strap is tightened. Still another disadvantage of such closure is that no means are provided for preventing circumferential movement of the strap before it is tightened.
It is also known in the art to provide a two-piece plastic closure comprising a split sleeve having threads on its inner peripheral surface. The split sleeve is placed on the pipe threads and a single sleeve is forced over the split sleeve to secure it to the pipe. A disadvantage of this closure is that the single sleeve is prone to slip off the split sleeve due to expansion and/or impact with or by foreign objects.
It is further known to provide metal closures having inner peripheral threads for threadedly engaging the external pipe threads. However, such metal closures suffer from the disadvantage that upon threading the closure onto the pipe end, cross threading may occur. Such cross threading may damage the external threads necessitating retapping or cutting off the damaged end and rethreading it. Another disadvantage of the metal closure is that rusting and corrosion may occur at the interface of the closure and pipe, or the parts will freeze together in winter necessitating the services of a welder to remove the rusted on or frozen closure.